Reversible time delay beamforming optical architecture for phased-array antennas

Abstract

A phased array antenna system has optical architecture comprising free space delay units and associated spatial light modulators compatible for operation with temporally incoherent or coherent laser light to produce signals having selected time delays to actuate antenna elements of an antenna array to transmit electromagnetic radiation at a selected beam angle from the phase array. The same optical architecture is used to process electromagnetic signals detected by the antenna array to produce an output signal for display or processing which corresponds to the radiation detected at the selected beam angle.

What is claimed is: 
     
       1. A phased array antenna system comprising: a plurality of antenna elements arranged in an array, said array being operable in a transmit or a receive mode;   an optical signal processing system coupled to said array, said system generating differentially time-delayed optical control signals to control output beam radiation patterns transmitted from said array and to optically process return radiation patterns detected by said array; and   a modulated laser source optically coupled to said signal processing system and having means for dividing light from said laser source into a plurality of collinear light beams;   said optical signal processing system comprising:   a plurality of spatial light modulators optically coupled to associated free space delay units so as to selectively time delay each of said plurality of light beams,   means for converting said optical control signals into corresponding electrical signals to excite said antenna elements in said transmit mode,   means for converting electrical signals produced by said antenna elements in response to detected electromagnetic radiation in said receive mode into corresponding return optical signals, and   means for converting said return optical signals after said optical processing into electrical signals.   
     
     
       2. The phased array antenna system of claim 1 wherein said means for dividing light from said laser source into a plurality of beams comprises a collimating lens. 
     
     
       3. The phased array antenna system of claim 1, wherein each of said free space delay units further comprises a pair of polarizing beam splitters optically coupled to a prism to provide a selected time delay to at least one of said plurality of light beams. 
     
     
       4. The phased array antenna system of claim 1 further comprising an optical adder to uniformly polarize each of said light beams emerging from said pluralilty of spatial light modulators and free space units. 
     
     
       5. The phased array antenna system of claim 4 wherein said optical adder comprises a spatial light modulator. 
     
     
       6. The phased array antenna system of claim 4 wherein said optical adder comprises a 45 degree oriented polarizer optically coupled to a half-wave plate. 
     
     
       7. The phased array antenna system of claim 6 further comprising a liquid crystal cell optically coupled to said half wave plate, said cell being coupled to selectively rotate the polarization orientation of incident light beams. 
     
     
       8. The phased array antenna system of claim 4 further comprising an input polarizing beam splitter to direct incident light of selected polarization orientations into said time delaying means. 
     
     
       9. The phased array antenna system of claim 4 further comprising an output polarizing beam splitter (PBS) optically coupled to receive light from said optical adder and optically coupled to transmit light of a first selected polarization orientation to said means for converting optical signals into corresponding electrical signals to excite said antenna elements and to transmit light of a second selected polarization rotation to said means for converting the processed optical return signals into electrical signals. 
     
     
       10. The phased array antenna system of claim 9 wherein said means for converting the processed return optical signals to electrical signals comprises a photodiode detector assembly. 
     
     
       11. The phased array antenna system of claim 10 wherein said photodiode detector assembly is optically coupled to said output polarizing beam splitter. 
     
     
       12. The phased array antenna system of claim 1 wherein said means for converting said optical control signals into corresponding electrical signals to excite said antenna elements comprises an array of photodiodes. 
     
     
       13. The phased array antenna system of claim 1 wherein said means for converting electrical signals generated by said array in said receive mode into corresponding return optical signals comprises an array of laser diodes. 
     
     
       14. The phased array antenna system of claim 1 wherein said light beams are comprised of temporally incoherent laser light. 
     
     
       15. The phased array antenna system of claim 1 wherein said light beams are comprised of coherent laser light. 
     
     
       16. The phased array antenna system of claim 1 wherein said modulated laser source comprises a semiconductor laser and means electrically coupled to said laser for direct linear modulation of said laser. 
     
     
       17. The phased array antenna system of claim 1 further comprising a transmit/receive switch to selectively electrically couple said antenna array to said means for converting optical control signals into corresponding electrical signals and to said means for converting electrical signals to corresponding optical return signals. 
     
     
       18. The phased array antenna system of claim 1 further comprising an array control computer coupled to said optical control system, said laser source, and said antenna array to control operation of said phased array antenna system in said transmit and said receive modes. 
     
     
       19. A phased array radar system comprising: an array control computer,   an antenna array having a plurality of elements, said array being operable in a transmit or receive mode,   a post detection display and analysis system,   a modulated laser source, and   an optical signal processing system electrically coupled to said antenna array and said post detection display and analysis system and optically coupled to said laser source,   said array control computer being coupled to said antenna array, said post detection display and analysis system, said modulated laser source and said optical signal processing system to control the combined operation thereof in said transmit and receive modes,   said signal processing system comprising: an optical architecture having an input polarizing beam splitter, a cascade of spatial light modulators and associated free space delay units to delay signals passing therethrough, said cascade being optically coupled to receive light beams from said input polarizing beam splitter, an optical adder optically coupled to said cascade to uniformly polarize light passing from said cascade, and an output polarizing beam splitter optically coupled to said adder,   an array of photodiodes to convert time delayed optical signals passing from said optical architecture into corresponding electrical signals,   an array of laser diodes to convert electrical signals generated by said antenna array in response to detected electromagnetic radiation into corresponding optical signals for application to said optical architecture, and   a detector assembly optically coupled to said optical architecture to convert said optical signals into an electrical output.     
     
     
       20. The phased array radar system of claim 19 wherein each of said spatial light modulators and associated free space delay units in said cascade produce a time delay of different duration. 
     
     
       21. The phased array radar system of claim 20 wherein said laser source produces temporally incoherent light.